Noble metals and rare metals are excellent in stability, catalytic activity, or the like, and are used industrially in a wide range of fields. However, those metals are rare and expensive resources, and are required to be utilized effectively. It is important to efficiently recover and reuse noble metals and rare metals contained in spent noble metal or rare metal-containing waste materials, such as waste material products and materials including waste catalysts for automobile exhaust gas purification, waste catalysts for chemical industry, waste products of electronic substrate manufacturing processes, scrap electronic parts, and electrolysis electrode scraps.
The typical method of recovering such noble metals and rare metals includes the wet method (hydrometallurgy) such as an acid dissolution method or a dry method (pyrometallurgy) using a molten metal (see Non-Patent Literature 1), and in both the cases, the noble metals and rare metals are eluted in a strong acid or a liquid phase of a molten metal.
{Non-Patent Literature 1}
Kikuo Fujiwara, “Recycle of noble metal”, Chemical Engineering, 55 (1), p. 21, 1991, The Society of Chemical Engineers, Japan